1. Field of the Invention
The present invention relates to a laser-excited plasma light source, and an exposure apparatus. More particularly, the present invention relates to a laser-excited plasma light source which generates an energy beam by irradiating an energy-ray generating material released from a nozzle with a laser beam to excite the energy-ray generating material to a plasma state, an exposure apparatus incorporating the laser-excited plasma light source and its making method, and a device manufacturing method for manufacturing micro-devices such as semiconductor devices using the exposure apparatus.
2. Description of the Related Art
EUV (Extreme Ultraviolet) exposure apparatus using EUV light having an wavelength within a range from 5 nm to 20 nm, for instance, 13 nm or 11 nm, as an exposure light, is currently being developed for use in a lithographic process for manufacturing semiconductor devices, as a generation after the next exposure apparatus which transfers, to a substrate (a wafer), a circuit pattern having a practical minimum line width (device rule) of 100 nm to 70 nm. Proposed as a first candidate for the exposure light source of the EUV exposure apparatus is a laser-excited plasma light source.
In conventional laser-excited plasma light sources chiefly employed, EUV light radiating material such as a copper tape is used as an energy-ray generating material (hereinafter referred to as a xe2x80x9ctargetxe2x80x9d as appropriate). And, a high-energy laser beam is condensed and directed onto the target to excite it to a plasma state to generate an energy beam such as an EUV light beam. Since, in spite of its compact size, the laser-excited plasma light source provides luminance as bright as that by undulators, the laser-excited plasma light source currently attracts attention as a light source for X-ray equipment such as an X-ray analysis apparatus or an X-ray exposure apparatus.
In the laser-excited plasma light source, besides energy beams, resulting from the destruction of the materials forming the target on which the plasma and the laser beam are converged, ions, atoms, and microscopic fragments are released. These sputtered particles, so-called debris, are stuck onto or deposited onto optical elements arranged close to the plasma (including a lens for condensing a laser beam, a collecting mirror for reflecting an energy beam generated from the plasma, i.e., an X ray, and a filter for transmitting the X ray generated from the plasma while cutting off visible light), thereby reducing the performance of the optical elements (reflectance and transmittance). The reduction of the sputtered particles is thus a major concern in the utilization of the laser-excited plasma light source.
To substantially reduce the sputtered particles, a gas cluster jet laser-excited plasma light source has been proposed (U.S. Pat. No. 5,577,092), in which a material (a high-density gas), remaining in a gaseous state at normal temperature, for instance, xenon (Xe), krypton (Kr), nitrogen, or carbon dioxide, is used and released through a nozzle, as a target, and the jet of this target gas or cluster is irradiated with a laser beam. Since the target remains gaseous at normal temperature, the target is not deposited in debris on the optical elements, and the performance of the optical elements is thus free from degradation.
The laser-excited plasma light source does not need a high level of vacuum (as high as 10xe2x88x929 Torr (10xe2x88x927 Pa) or so), and the vacuum level is sufficient if the laser beam does not perform gaseous release in residual gas prior to reaching the target and if the energy beam generated from the plasma is free from high absorption prior to reaching an object to be irradiated. Specifically, a vacuum of several tens of Torr to 0.1 Torr (8,000 Pa-10 Pa) is acceptable. For this reason, a low-cost evacuator, such as a rotary pump, works, and is thus reasonable for use.
In the gas cluster jet laser-excited plasma light source referenced above, the jet of the gas from the nozzle freely expands in the vacuum, and the density of the gas rapidly drops as the gas distances from the nozzle. To increase the dose of the energy beam from the plasma, the plasma has to be generated close to the nozzle (within a distance of several tenths mm to several mm) where the density of the gas (cluster) is still high. When the plasma is generated close to the nozzle, fast atoms, ions and electrons emitted from the plasma collide with nearby components, and erode these components. Atomic or fragmental debris eroded from the nozzle and components peripheral to the nozzle (hereinafter referred to as sputtered particles) scatter in all directions, and are adhered and deposited on the optical elements arranged close to the plasma, causing a drop in the performance of the optical elements.
To increase an energy conversion efficiency from the laser beam to the energy beam such as an X ray in the gas cluster jet laser-excited plasma light source, the plasma has to be located somewhat closer to the nozzle. But locating the plasma close to the nozzle increases sputtered particles from the nozzle and the components close to the nozzle. This method in the laser-excited plasma light source cannot satisfy the two requirements at the same time, namely the improvement in the energy conversion efficiency and the reduction in the sputtered particles.
Also, according to recent studies, even with a minimum distance of several mm between the laser converging point and the end of the nozzle, the plasma becomes extremely hot and erodes and damages the spout at the end of the nozzle, scattering heavy metal which constitutes the end of the nozzle. It then becomes some sort of debris, and the debris is deposited on the collecting mirror, degrading the reflectance of the collecting mirror.
Presumably, the same phenomenon takes place in the laser-excited plasma light source disclosed in U.S. Pat. No. 5,577,091 and U.S. Pat. No. 5,459,771, in which ice crystals and snow flakes are used as a target.
Although it is a small amount, oil used in the rotary pump is reversed to the vacuum system, and is adhered and deposited on the optical elements during long time of use, thereby gradually decreasing the performance of the optical elements (i.e., reflectance, transmittance, and diffraction efficiency) in time. To cope with this problem, the apparatus needed to be disassembled to replace an affected optical element with a new one, or an affected optical element had to be cleaned and put back in place.
In an EUV exposure apparatus using the above-referenced gas cluster jet laser-excited plasma light source, the life of a collecting mirror is shortened by the generation of debris or the reverse flow of the oil, and a maintenance job, such as the replacement of the collecting mirror, has to be frequently performed. For each maintenance job, the apparatus needs to be stopped.
The present invention has been developed in view of the above problems, and it is a first object of the present invention to provide a laser-excited plasma light source which reduces a drop in the reflectance of a collecting mirror due to the generation of debris.
A second object of the present invention is to provide an exposure apparatus which reduces the frequency of maintenance jobs, such as the replacement of the collecting mirror, and improves the production yield of devices.
The present invention in a first aspect lies in a first laser-excited plasma light source which generates energy beams by irradiating an energy-ray generating material with a laser beam to excite the energy-ray generating material to a plasma state, the light source comprising: a nozzle which releases the energy-ray generating material, and at least a surface layer of an end portion of the nozzle is formed of a material including a specific material, the specific material having a transmittance larger than that of a heavy metal to an energy beam which has a wavelength to be utilized, the energy beam being among the generated beams; and a laser light source which irradiates the energy-ray generating material released through the nozzle with the laser beam.
In this description, xe2x80x9cmaterials including a specific materialxe2x80x9d collectively refer to a specific material, a compound or a mixture, which includes the specific material as a principal constituent.
In this arrangement, the energy-ray generating material is excited to a plasma state and the energy beam is generated, when the energy-ray generating material is released through the nozzle, and is then irradiated with the laser beam. When the energy beam is generated, at least the surface layer of the end of the nozzle is eroded by the high temperature of the plasma, or by the collision of atoms, ions, and electrons created from the plasma. At least the surface layer of the end of the nozzle is formed of the materials including the specific material having the transmittance, higher than those of the heavy materials, to the energy beam in use. The temperature of the end of the nozzle may become higher than the melting point of the specific material because of the high temperature of the plasma. Even if the end of the nozzle is eroded, and the sputtered particles are deposited on the nearby collecting mirror, the rate of reduction in the reflectance of the collecting mirror is reduced in comparison with the case in which a conventional heavy metal nozzle is employed, because the transmittance of the sputtered particles (containing specific material) to the energy beam is higher than that of the heavy metal.
In the first laser-excited plasma light source of the present invention, the energy beam to be utilized may be EUV (Extreme Ultraviolet) light having a wavelength within a range from 5 nm to 50 nm. In this case, the specific material is preferably one of silicon (Si) and beryllium (Be). Silicon has a transmittance higher than those of heavy materials, to the EUV light as an energy beam, and a thickness of 0.5 xcexcm of silicon layer transmits the EUV light at a transmittance of 50% or so, and beryllium has a transmittance as high as or higher than that of silicon. Even if these elements become sputtered particles and are deposited on the collecting mirror, a drop in the reflectance thereof due to the deposits remains small.
In the first laser-excited plasma light source of the present invention, the end portion of the nozzle is formed of only the specific material, or alternatively, the surface layer of the end portion of the nozzle may be formed of a coating layer of the specific material deposited on a surface of a base member. In the latter case, the base is preferably formed of a metal, such as iron (Fe), titanium (Ti), tungsten (W), or an alloy, or carbon, and is more preferably formed of a high-melting point metal such as tungsten (W) or carbon. Since these metals are easier to process than silicon, the manufacturing of the nozzle is easy, and tungsten (W) has an excellent heat resistance.
In the first laser-excited plasma light source of the present invention, water or ice may be employed as the energy-ray generating material, and the energy-ray generating material may be one of a gas and clusters. The use of these materials as an energy-ray generating material substantially reduces the sputtered particles. A xenon gas may also be employed as an energy-ray generating material.
In the first laser-excited plasma light source of the present invention, a vacuum chamber that encloses the nozzle and members peripheral to the nozzle may be included. This arrangement not only reduces a reduction in the reflectance of the optical elements close to the nozzle, but also reliably prevents the above-mentioned sputtered particles from depositing on the collecting mirror arranged external to the vacuum chamber. In this case, at least the surface layer of the nozzle and at least a surface layer of at least one of the peripheral members may be formed of materials including the specific material. Since, the surface of the peripheral members is subject to an erosion (is subject to an abrasion) as a result of the high temperature of the plasma and the collision of atoms, ions, and electrons created from the plasma like the surface layer of the nozzle end portion, the reduction in the reflectance is controlled when the sputtered particles are deposited onto the collecting mirror.
When the vacuum chamber that encloses the nozzle and members peripheral to the nozzle is included, the first laser-excited plasma light source of the present invention may further include at least one multilayer film mirror which has a multilayer film formed on its reflective surface, and is arranged as one of a portion of the vacuum chamber and inside the vacuum chamber, wherein the specific material can be a material selected from among materials employed for the multilayer film which has a high transmittance to the energy beam.
A multilayer film, formed on the mirror reflective surface on which an energy beam having a short wavelength, for instance, a n X ray, is radiated from the laser-excited plasma light source, is formed of a combination of a material having a high complex index of refraction and a material having a high transmittance at a reflected wavelength. Considering this point in the present invention, the specific material, namely, a chief constituent of the materials forming at least the surface layer of the nozzle end portion and the peripheral members, subject to erosion as a result of the high temperature of the plasma and the collision of atoms, ions, and electrons created from the plasma against the layer, is a material selected from among materials employed for the multilayer film which has a high transmittance to the energy beam.
Specifically, even if the materials, including such a specific material, become the sputtered particles, and are deposited on the multilayer film mirrors including the collecting mirror, the drop in the reflectance of the multilayer film mirror such as the collecting mirror is marginal and a drop in the output intensity of the energy beam also remains marginal, because most of the components of the sputtered particles is the original constituent forming the multilayer film.
When the vacuum chamber includes a plurality of optical elements, such as the multilayer film mirror, and thin-film materials are different from optical element to optical element, it is preferred to use a thin-film material having the highest transmittance to the energy beam having a wavelength in use and being appropriate as a material for the nozzle and the members peripheral to the nozzle.
In this case, the multilayer film mirror may be an optical element on which the energy beam generated from the plasma is first incident (for convenience, referred to as a xe2x80x9cfirst optical elementxe2x80x9d). The first optical element is most subject to the influence of the sputtered particles. In accordance with the present invention, the drop in the reflectance of the first optical element is controlled in the way discussed above, and the drop in the output strength of the energy beam is consequently controlled.
The present invention in a second aspect lies in a second laser-excited plasma light source which generates an energy beam by irradiating an energy-ray generating material with a laser beam to excite the energy-ray generating material to a plasma state, the light source comprising: a nozzle which releases the energy-ray generating material; a vacuum chamber which encloses the nozzle and members peripheral to the nozzle; and a laser light source which irradiates the energy-ray generating material being released through the nozzle, with the laser beam, wherein the energy beam is an X-ray, and at least a surface layer of an end of the nozzle and the peripheral members is formed of a material including at least one material selected from a group consisting of beryllium (Be), boron (B), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), argon (Ar), krypton (Kr), rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), ruthenium (Ru), rhodium (Rh), palladium (Pd), and silver (Ag).
In the laser-excited plasma light source in which the energy beam to be utilized is an X ray, krypton (Kr) and xenon (Xe) are frequently used as the energy-ray generating material (hereinafter referred to as a xe2x80x9ctargetxe2x80x9d as appropriate). The above-mentioned material, such as beryllium (Be), has a high transmittance to an X ray (more precisely, EUV light within the soft X-ray region) in a wavelength range from 10 to 13 nm when krypton (Kr) or xenon (Xe) is used as an energy-ray generating material. As in the second laser-excited plasma light source, the drop in the reflectance when the sputtered particles are deposited on the collecting mirror is controlled by forming, of materials including beryllium (Be) or the like, at least the surface layer of the nozzle end portion and the peripheral members thereof, subject to the erosion as a result of the high temperature of the plasma and the collision of atoms, ions, and electrons created from the plasma against the layer.
The present invention in a third aspect lies in a third laser-excited plasma light source which generates an energy beam by irradiating an energy-ray generating material with a laser beam to excite the energy-ray generating material to a plasma state, the light source comprising: a nozzle which releases the energy-ray generating material; a vacuum chamber which encloses the nozzle and members peripheral to the nozzle; a laser light source which irradiates the energy-ray generating material being released through the nozzle, with the laser beam; at least one optical element arranged as one of a portion of the vacuum chamber and inside the vacuum chamber; a first mechanism which irradiates at least one of the optical elements with light having a wavelength not longer than 400 nm; a second mechanism which introduces a gas containing at least one of oxygen and ozone, at least close to the optical element irradiated with the light within the vacuum chamber, wherein among the nozzle and the peripheral members, at least a surface layer of an end portion of the nozzle is formed of materials including carbon.
Light rays of 400 nm or shorter include ultraviolet light, vacuum ultraviolet light and light having a wavelength shorter than the wavelengths of these. The xe2x80x9cgas containing at least one of oxygen and ozonexe2x80x9d may be a gas containing oxygen, a gas containing ozone, a gas containing both oxygen and ozone, oxygen itself, or ozone itself. The xe2x80x9cmaterials including carbonxe2x80x9d may be a compound or a mixture having carbon as the chief constituent thereof, or carbon itself.
In accordance with the present invention, the energy-ray generating material is released through the nozzle. When the released energy-ray generating material is irradiated with the laser beam, the energy-ray generating material is excited to a plasma state, generating an energy beam. When the energy beam is generated, the surface layer of the end of the nozzle is eroded by the high temperature of the plasma, or the collision of atoms, ions, and electrons created from the plasma against the layer, and the sputtered particles are deposited on the collecting mirror and other optical elements in the vacuum chamber. The first mechanism irradiates at least one of the optical elements arranged as a portion of or within the vacuum chamber (specifically, an optical element from which the sputtered particles need to be removed), with light having a wavelength not longer than 400 nm, and the second mechanism introduces the gas containing at least one of oxygen and ozone, at least close to the optical element irradiated with the light within the vacuum chamber.
Since in this case, the surface layer of the nozzle end portion most subject to erosion by the high temperature of the plasma or the collision of the atoms, ions, and electrons created from the plasma against the layer, is formed of the materials containing carbon, the sputtered particles are also made of the materials containing carbon. For this reason, the first mechanism irradiates, with the light having a wavelength not longer than 400 nm, the optical element from which the sputtered particles need to be removed and the second mechanism introduces the gas containing at least one of oxygen and ozone close to the optical element or entirely within the vacuum chamber. Carbon in the sputtered particles stuck onto the surface of the optical element reacts with oxygen or ozone, becoming carbon monoxide (CO) or carbon dioxide (CO2), and thereby removing the sputtered particles. The reason why the light having the wavelength not longer than 400 nm is to facilitate the reaction of oxygen through radical formation, or to break a chemical bond by imparting energy to a chemical bond in the sputtered particles. For this reason, this arrangement is particularly effective when the sputtered particles contain an organic compound or when oil or the like, reversely circulated from a vacuum pump, is deposited on the optical element. In this case, carbon or hydrogen with the chemical bond broken reacts with radical oxygen or ozone, becoming carbon monoxide (CO), carbon dioxide (CO2), water (H2O), and thereby being removed from the optical element. The third laser-excited plasma light source of the present invention can restore the strength of the energy beam within a short period of time, without the need for the disassembling of the apparatus for the replacement or cleaning of the optical element.
In the third laser-excited plasma light source of the present invention, the second mechanism may adjust a pressure interior of the vacuum chamber within a range of several hundredths of Torr to several tens of Torr (1 Pa-8,000 Pa) when the gas is introduced. When the energy beam having the required wavelength is an X ray (EUV light) within a wavelength range from 5 to 15 nm, from among the energy beams generated from the plasma, the attenuation of the X ray is sufficiently small in the vacuum chamber having the pressure of this level, and the attenuation of light (ultraviolet light) having the wavelength not longer than 400 nm is sufficiently small, and the ultraviolet light having a sufficient strength reaches the optical element from which the sputtered particles need to be removed. Furthermore, a sufficient amount of oxygen molecules (or ozone generated from oxygen by ultraviolet light) which may react with the carbon contained in the deposited sputtered particles is present close to the surface of the optical element. Since the attenuation of the energy beam having the required wavelength is sufficiently small, the irradiation with the laser beam can be quickly resumed even if the irradiation with the laser beam from a laser light source is once suspended to remove the deposit on the surface of the optical element.
In the third laser-excited plasma light source of the present invention, the first mechanism is preferably arranged so it can irradiate the optical element with the light without blocking off an outgoing energy beam radiated from the plasma which proceeds out of the vacuum chamber, the outgoing energy beam being the energy beam. With this arrangement, the deposit on the surface of the optical element is removed without the need for the suspension of the irradiation with the laser beam from the laser light source, and the collecting mirror maintains the reflectance thereof for a long period of time, and an extremely long-time continuous operation thus becomes possible.
In the third laser-excited plasma light source of the present invention, the second mechanism can have a cover which is detachably engaged with the optical element irradiated with the light by the first mechanism and substantially seals an interior of the cover, the second mechanism introducing the gas into the interior of the cover. In the second mechanism, the cover is attached to the optical element, irradiated with the light by the first mechanism and the gas containing at least one of oxygen and ozone is supplied into the internal space of the cover only. Since the cover substantially seals the interior, the gas is prevented from leaking out into the vacuum chamber external to the cover, and the light from the first mechanism is not absorbed by oxygen outside the cover. Stronger light thus reaches the optical element. Since the pressure inside the cover can be set to be higher than the pressure within the vacuum chamber without the cover, the removal of carbon-based deposits stuck on the optical element is performed within a shorter duration of time.
In the third laser-excited plasma light source of the present invention, the optical element irradiated with the light by the first mechanism may be an optical element on which the energy beam radiated from the plasma is first incident. As already discussed, the first optical element is most subject to the influence of the sputtered particles. In accordance with the present invention, for the reason described above, the sputtered particle deposits stuck on the first optical element are decomposed and removed, and the drop in the strength of the energy beam is efficiently avoided.
In the third laser-excited plasma light source of the present invention, the materials containing carbon may be one of diamond and an organic compound. In such a case, the surface layer of the nozzle end portion, most likely to be abraded by the atoms, ions, and electrons released from the plasma, is formed of carbon only, and is formed of diamond, which is one of the hardest substances, or the high-hardness organic compound. The rate of abrasion of the nozzle end portion is thus extremely small, and the amount of the sputtered particles is also extremely small. Even if the sputtered particles are deposited on the optical element, carbon stuck on and deposited on the optical element is easily removed by the above means. As the organic compound Kevlar (aromatic species) having a high hardness may be employed. A portion other than the nozzle end portion, and the members peripheral to the nozzle may also be constructed of diamond or the like.
In the third laser-excited plasma light source of the present invention, at least one of the optical elements may be a multilayer film mirror which has a multilayer film formed on its reflective surface, and the materials including carbon are one of a compound and a mixture of carbon and a material selected from among materials used for the multilayer film which has a high transmittance to the energy beam. In this arrangement, the sputtered particles are the compound or the mixture of carbon and the material selected from among materials employed for the multilayer film and having a high transmittance to the energy beam. As already described, carbon is removed when reacting with oxygen. Even if materials other than carbon remain, the materials are the ones employed for the multilayer film and exhibiting a high transmittance to the energy beam having the wavelength in use, and the attenuation of the X ray is small. The multilayer film mirror maintains a sufficient reflectance for a long period of time, and the third laser-excited plasma light source of the present invention can restore the strength of the energy beam within a short period of time, without having to disassemble the apparatus for the replacement or cleaning of the optical element.
The third laser-excited plasma light source of the present invention may further include a heating device which heats the optical element irradiated with the light by the first mechanism. With this arrangement, the reaction of carbon with a gas, such as oxygen, is expedited by heating the optical element irradiated with the ultraviolet light or the like with the heating device.
In the second and third laser-excited plasma light sources of the present invention, water or ice may be employed as the energy-ray generating material, and the energy-ray generating material maybe a gas or clusters. The use of these materials as an energy-ray generating material substantially reduces the sputtered particles.
The present invention in a fourth aspect lies in a fourth laser-excited plasma light source which generates an energy beam by irradiating an energy-ray generating material with a laser beam to excite the energy-ray generating material to a plasma state, the light source comprising: a nozzle which releases the energy-ray generating material; an optical element which reflects the energy beam; wherein at least a surface layer of the nozzle is formed of a specific material employed for a reflective surface of the optical element.
With this arrangement, the energy-ray generating material is released through the nozzle. When the released energy-ray generating material is irradiated with the laser beam, the energy-ray generating material is excited to a plasma state, generating an energy beam. When the energy beam is generated, at least the surface layer of the nozzle, particularly, the surface layer of the end of the nozzle, is eroded by the high temperature of the plasma, or the collision of atoms, ions, and electrons created from the plasma against the layer, and the sputtered particles are deposited on the optical elements which reflect the energy beam. Since at least the surface layer of the nozzle end portion is formed of the specific material employed for the reflective surface of the optical element, the sputtered particles are also formed of the specific material. Even if the sputtered particles are deposited on the optical element, the reflectance of the optical element to the energy beam suffers from almost no drop, and the drop in the output strength of the energy beam becomes marginal.
In the fourth laser-excited plasma light source of the present invention, when the optical element comprises a multilayer film on the reflective surface of the optical element, the specific material is preferably selected from materials employed for the multilayer film. With this arrangement, the specific material selected from materials employed for the multilayer film becomes the sputtered particles, and even if the sputtered particles are deposited on the optical element, the drop in the reflectance of the optical element having the multilayer film on the reflective layer thereof is marginal, because most of the constituents of the sputtered particles are the original constituent forming the multilayer film.
The present invention in a fifth aspect lies in a fifth laser-excited plasma light source which generates an energy beam by irradiating an energy-ray generating material with a laser beam to excite the energy-ray generating material to a plasma state, the light source comprising: a nozzle which releases the energy-ray generating material; a container which houses the nozzle; an optical element arranged as one of a portion of the container and inside the container; and an optical cleaning mechanism which introduces a gas containing at least of one of oxygen and ozone close to at least the optical element within the container, and irradiates the optical element with a cleaning light.
With this arrangement, the energy-ray generating material is released through the nozzle. When the released energy-ray generating material is irradiated with the laser beam, the energy-ray generating material is excited to a plasma state, generating an energy beam. When the energy beam is generated, the surface layer of the end of the nozzle is eroded by the high temperature of the plasma, or the collision of atoms, ions, and electrons created from the plasma against the layer, and the sputtered particles are deposited on the optical elements in the container. The optical cleaning mechanism introduces the gas containing at least of one of oxygen and ozone, at least close to the optical element within the container, and irradiates the optical element with cleaning light. The sputtered particles deposited on the optical element is removed through the cleaning effect of ozone which is generated through photochemical reaction of oxygen contained in the introduced gas with the cleaning light, or of ozone contained in the gas. The energy of the cleaning light breaks the chemical bond in the sputtered particles.
In the fifth laser-excited plasma light source of the present invention, the cleaning light preferably has a wavelength not longer than 400 nm. In this arrangement, the cleaning light with the energy produces oxygen radicals from oxygen to accelerate reaction, or breaks the chemical bond by imparting energy to the chemical bond in the sputtered particles. For this reason, this arrangement is particularly effective when the sputtered particles contain an organic compound or when oil or the like, reversely circulated from a vacuum pump, is deposited on the optical element.
In the fifth laser-excited plasma light source of the present invention, at least a surface layer of the nozzle preferably is formed of materials containing carbon. Since in such a case, the surface layer of the nozzle end portion, most likely to be eroded by the high temperature of the plasma or the collision of the atoms, ions, and electrons created from the plasma against the layer, is formed of the materials containing carbon, the sputtered particles are also formed of the materials containing carbon. For this reason, during the above-mentioned optical cleaning operation, carbon in the sputtered particles deposited on the surface of the optical element reacts with oxygen or ozone, and becomes monoxide (CO) or carbon dioxide (CO2), and the sputtered particles are easily removed.
The present invention in a sixth aspect lies in an exposure apparatus which transfers a pattern formed on a mask onto a substrate while synchronously moving the mask and the substrate, the exposure apparatus comprising: a laser-excited plasma light source according to the present invention; an illumination optical system which illuminates the mask with an energy beam emitted from the laser-excited plasma light source; a mask stage which holds the mask; a projection optical system which projects the energy beam emitted from the mask to the substrate; a substrate stage which holds the substrate; and a driving system which drives the mask stage and the substrate stage.
With this arrangement, the illumination optical system illuminates the mask with the energy beam generated from the laser-excited plasma light source of the present invention, and the projection optical system projects the energy beam from the mask to the substrate. In this state, the driving system drives the mask stage and the substrate stage so that the mask and the substrate move in synchronization, and a pattern formed on the mask is thus projected and transferred to the substrate. Due to the operation of the laser-excited plasma light source of the present invention, the drop in the reflectance of the collecting mirror is reduced, the frequency of maintenance jobs for the replacement or the like for the collecting mirror is reduced, and the downtime of the apparatus is reduced and the production yield of devices is improved.
The present invention in a seventh aspect lies in a making method of an exposure apparatus used in a lithographic process, the method comprising: providing a laser-excited plasma light source according to the present invention; providing an illumination optical system which illuminates a mask with an energy beam emitted from the laser-excited plasma light source; providing a mask stage which holds the mask; providing a projection optical system which projects the energy beam emitted from the mask to a substrate; providing a substrate stage which holds the substrate; and providing a driving system which drives the mask stage and the substrate stage.
With this arrangement, the exposure apparatus of the present invention is made by mechanically, optically, and electrically combining and adjusting the laser-excited plasma light source of the present invention, the illumination optical system, the projection optical system, the substrate stage, the mask stage, the driving system, and a diversity of other components. In this case, a step-and-scan scanning exposure apparatus is made.
When exposure is performed by the exposure apparatus of the present invention in the lithographic process, a fine pattern as fine as a device rule of 100 nm to 70 nm is precisely transferred using exposure illumination light such as EUV light generated by the laser-excited plasma light source. By reducing the downtime of the apparatus for maintenance jobs for the collecting mirror or the like, the operation ratio of the apparatus is improved. Micro-devices having a high degree of integration are manufactured with a high production yield. From a different point of view, the present invention lies in a device manufacturing method employing the exposure apparatus of the present invention.